avformat/mov: Enable stream parsing for VP9.

MP4 media containing VP9 using superframes (such as
https://github.com/Netflix/vp9-dash/raw/master/DASH-Samples/Fountain_2997_0560kbps_640x480_4x3PAR.ivf_DashUnencrypted.ismv

)
does not decode correctly with the built-in VP9 decoder because
superframes are passed to the decoder whole rather than split into
individual frames.

Signed-off-by: Matthew Gregan <kinetik@flim.org>